The present invention relates to a method for controlling a capacitive anti-trap system and to a capacitive anti-trap system.
In the case of vehicle closing elements which are displaceable increasingly actuated by external force, in particular driven by a motor, there is a considerable risk during closing of the respective vehicle closing element of a body part of a person standing close to the vehicle being trapped, for example, which can result in considerable injury. For this reason, in capacitive anti-trap systems which are well known per se for vehicles, in particular for motor vehicles, an obstacle in the displacement path of a vehicle closing element to be closed driven by a motor is detected contactlessly by a changing electrical capacitance and an obstacle is prevented from being trapped between the closing vehicle closing element and a vehicle structure in the region of a vehicle body opening which is intended to be closed by the vehicle closing element in a closed position. Such a vehicle closing element may be, for example, a side door, a tailgate, a trunk lid, a window pane or a sliding roof of a motor vehicle.
In comparison with purely tactile anti-trap systems, anti-trap systems with capacitive identification have the advantage that any obstacle can be determined even before contact with the vehicle closing element or even shortly thereafter without a certain force needing to act on the sensor system of the anti-trap system in order that the system is triggered and the displacement movement of the vehicle closing element is stopped and/or reversed.
In the case of capacitive anti-trap systems on which the present invention is based, use is made of the fact that, in the case of an electrode arrangement of the anti-trap system consisting of at least one transmission electrode and one reception electrode, a signal which is characteristic of the presence of an obstacle can be received at the reception electrode when the transmission electrode is actuated by alternating electric current. Thus, owing to actuation of the transmission electrode by alternating current, an electrical field is generated which is influenced by an obstacle such that an electrical capacitance is measurably changed. This measurable change in the electrical capacitance is measurable at the reception electrode, which is arranged spaced apart from the transmission electrode, and can be evaluated on the basis of a signal received from the measurement electrode, generally a voltage signal, in order to trigger the anti-trap system and to influence the displacement movement of the vehicle closing element.
In the case of a vehicle closing element with a comparatively large area, such as, for example, a tailgate of a motor vehicle, generally a plurality of electrode arrangements are provided spaced physically apart from one another in order to monitor precisely regions in which the trapping of an obstacle is particularly critical in a targeted manner. It is also possible for easier fitting for individual electrode arrangements to be constructed separately from one another.
For example, US 2007/0035156 A1 describes an anti-trap system in which two electrode arrangements, each having a transmission electrode and a reception electrode, are provided on mutually opposite closing edges, on the longitudinal side, of a vehicle tailgate. The individual electrode pairs define in each case one monitoring region on a closing edge of the tailgate in which an obstacle in the displacement path of the closing tailgate is detectable. The actuation and evaluation the two electrode pairs in this case takes place separately, in each case. An electronic evaluation unit of the anti-trap system from US 2007/0035156 A1 therefore always receives at least two signals, on the basis of which the electronic evaluation unit needs to draw a conclusion on the presence of an obstacle in one monitoring region or the other.
However, such a separate evaluation in respect of the presence of an obstacle in different monitoring regions can be comparatively complex, on the one hand, and can make a capacitive anti-trap system comparatively slow, on the other hand. Thus, in the case of capacitive anti-trap systems which only provide a single signal generator by means of which the respectively used transmission electrodes are actuated by an alternating electric current of predetermined amplitude and frequency for reasons of costs, for example, (measurement) signals received at the reception electrode or the reception electrodes can only be evaluated by an electronic evaluation unit in temporal succession in order to determine a possible obstacle in the displacement path of the vehicle closing element.